Psychology, Public Policy, and Law, Vol 32(3), Aug 2026, 245-261; doi:10.1037/law0000488
When sexual offenses are tried in criminal court, it is common for multiple complainants (i.e., alleged victims who are witnesses) to testify against the same defendant in a single trial, known as “trial joinder.” When complainants are joined at trial, often the law requires that they be evaluated independently, but based on a psychological literature of context effects, multiple complainants testifying in the same trial violates this assumption of independence. Across two studies, this research examined judicial outcomes of sexual offenses when trials were joined. In Study 1, we explored the real-world relationship between the number of complainants at trial and verdict using a dataset of 4,237 Canadian criminal cases of child sexual abuse. Descriptively, the data showed a nonlinear pattern whereby conviction rate increased, peaked, and then decreased as the number of complainants at trial increased. Using an experimental paradigm in Study 2, we replicated the same nonlinear pattern predicting mock jurors’ perceptions of guilt; however, the effect was not observed when predicting complainant credibility. Consistent with the joinder effect literature, the current research suggests that trial joinder has a biasing effect on perceptions of guilt in sexual assault cases. Extending the literature, the current research also suggests the pattern of guilt bias may be more complex than initially thought. The research is aligned, however, in that trial joinder risks judicial fairness by altering perceptions of guilt due to irrelevant factors. Implications for justice policy are discussed. (PsycInfo Database Record (c) 2026 APA, all rights reserved)